1. Field of the Invention
The invention relates to a medical device with a needle cannula and a shield for passively shielding the needle cannula.
2. Description of the Related Art
A typical needle assembly includes a needle cannula having a proximal end, a pointed distal end and a lumen extending between the ends. A thermoplastic hub is mounted securely to the needle cannula at a location spaced from the distal end. The hub is provided with external threads or other surface configurations for removably mounting the prior art needle cannula on another structure. Some needle assemblies are used for drawing a sample of blood or other body fluid from a patient. The needle cannulas for these assemblies typically have pointed proximal and distal ends, and the needle hub is mounted to a location between the opposed ends of the needle cannula.
A needle assembly that is used to draw a sample of blood or other bodily fluid typically is used with a needle holder. The needle holder has a substantially tubular sidewall with a widely opened proximal end and a partly closed distal end. The hub of the prior art needle assembly can be engaged releasably with the partly closed distal end of the needle holder. Thus, the pointed proximal end of the needle cannula projects into the needle holder, while the pointed distal end of the needle cannula projects distally beyond the needle holder.
The combination of a needle assembly and a needle holder is used with an evacuated tube for drawing a sample of blood or other bodily fluid from a patient. The tube has a closed end, an open end, and a sidewall extending between the ends. The tube is evacuated, and the open end is sealed by a septum that retains the vacuum within the tube. The evacuated tube is dimensioned to be slid into the open proximal end of the needle holder. Sufficient sliding of the evacuated tube into the needle holder causes the proximal point of the needle cannula to pierce the septum of the evacuated tube. Thus, the needle cannula can be placed in communication with the interior of the evacuated tube.
The combination of a needle assembly, a needle holder and an evacuated tube is employed by initially urging the pointed distal end of the needle cannula into a blood vessel of a patient. Once the targeted blood vessel has been reached, the evacuated tube is urged into the needle holder so that the proximal point of the needle cannula pierces the septum on the tube. Low pressure conditions within the evacuated tube generate a flow of blood from the patient through the needle cannula and into the evacuated tube. The evacuated tube may be removed from the needle holder after a sufficient quantity of blood has been collected. One or more additional evacuated tubes may similarly be urged into the open end of the needle holder for drawing one or more additional samples of blood to be analyzed.
The needle cannula is withdrawn from the patient after a sufficient volume of blood has been collected for the required analytical procedures. The used needle cannula then must be shielded properly to avoid an accidental stick that could transmit a disease from the patient to the medical practitioner.
Many types of devices are available for shielding a used needle cannula. Some shields are hinged to the needle hub, and can be rotated from a first position, where the hinged shield is spaced from the needle cannula for use. After use, the hinged shield is rotated to a second position in shielding engagement around the needle cannula.
Other shields are telescoped over both the needle cannula and the needle hub. These shields initially are retained in a proximal position where the shield covers the hub but exposes the needle cannula for use. After use, the shield is telescoped distally to cover the needle cannula.
Most shielded needle assemblies are effective at performing their primary function of shielding a used needle cannula. However, many medical practitioners consider the available shieldable needle assemblies cumbersome. In particular, the shield that is telescoped over the needle hub typically will move relative to the needle cannula. Consequently, medical practitioners will grip the needle holder or other medical implement to which the shieldable needle assembly is mounted. However, a gripable region on the needle holder typically is relatively far from the distal end of the needle cannula and leads to at least a perception of poor control of the needle cannula. The perception of poor control increases as the length of the needle cannula is increased. As a result, needle assemblies with shields that telescope over the needle hub necessarily impose a limit on the length of the needle cannula that can be employed.
Additionally, in some cases, practitioners may be rushing and forget to operate the safety shield. Other situations arise where the patient moves suddenly or unexpectedly. Thus the needle cannula may inadvertently be pulled out of the vein and exposed with no time for the phlebotomist to initiate safety shielding. These weaknesses are not addressed adequately in prior art devices.
Successful venous entry depends partly upon the depth and angle of insertion of the needle cannula. A needle cannula that is inserted insufficiently may not reach a targeted blood vessel. Alternatively, a needle cannula can be inserted completely through a targeted blood vessel. Medical practitioners often judge the depth and angle of insertion of a needle cannula by monitoring the portions of the needle cannula that remain exposed between the skin of the patient and the hub of the needle assembly. The removal of a blood collection tube from a needle holder and the insertion of a new blood collection tube into the needle holder create forces along the axis of the needle cannula. These forces have the potential for varying the depth of insertion of the needle cannula. Accordingly, most medical practitioners monitor the section of the needle cannula that is exposed each time a blood collection tube is removed from the needle holder or inserted into the needle holder. Safety shields can impede the ability to visually monitor the depth of insertion of a needle cannula. Accordingly, an optimal safety shield will provide adequate safety against accidental sticks without obscuring the medical practitioner's view of the needle cannula between the skin of the patient and a reference point at or near the hub of the needle cannula.